Mobile communication systems were developed to provide mobile users with communication services. With the rapid advance of technologies, the mobile communication systems have evolved to the level capable of providing high speed data communication service beyond the early voice-oriented services.
Recently, standardization for a Long Term Evolution (LTE) system, as one of the next-generation mobile communication systems, is underway in the 3rd Generation Partnership Project (3GPP). LTE is a technology for realizing high-speed packet-based communications with the data rate of up to 100 Mbps, which is higher than the currently available data rate, and its standardization is almost complete. In line with the completion of the standardization of LTE, the discussion focus is shifted to LTE-Advanced (LTE-A) for increasing the data rate by adopting new technologies. The term ‘LTE system” as used herein may be construed to include the legacy LTE system and the LTE-A system.